Look for journalistic standards of reporting. High-quality, investigative news sources have explicit editorial policies and follow a code of ethics or professional standards. Examples: Society of Professional Journalists (SPJ) Code of Ethics; Ethical Journalism Network's 5 Principles of Ethical Journalism.
Does the news source you are using have an explicit Editorial Policy?
Does it follow a Code of Ethics?
Lack of an explicit and prominent editorial policy or a statement of ethical standards is a red flag indicating suspect content.
American Society of News Editors (ASNE) links to individual news sources codes of ethics and newsroom practice.
Specific examples from the ASNE website:
Los Angeles Times Ethics Guidelines
Hearst Newspapers: Statement of Professional Principles
Accountable sources issue corrections for errors and inaccuracies they subsequently discover. Fake news sources are not accountable for their content. Fake news creates or uses content that is partially fabricated or contain misleading information as well as outright falsehoods.
Accountable sources sign their stories and take personal responsibility for the content.
Articles should have bylines (the names of the authors). An individual or group of individuals take personal and professional responsibility for the accuracy of the information in the article. Lack of a byline is a red flag indicating suspect content.
Click on the byline if it's linked. Where does it lead?
Google the author names. Is there a LinkedIn profile? some other form of biographical information? What has the author done in the past? Does the author's background and experience qualify her or him to write on the article topic?